Current zero sensing and latching element for circuit breakers



Dec. 27, 1966 H. RSHAFFER ETAL CURRENT ZERO SENSING AND LATCHING ELEMENT FOR CIRCUIT BREAKERS 2 Sheets-Sheet 1 Filed Aug. l2. 1965 DSG 27, 1965 H. R. SHAFT-ER ETAL 3,295,077

CURRENT ZERO sENsINC AND LATCHINC ELEMENT FCR CIRCUIT BREAKERS Filed Aug'. l2, 1965 2 Sheets-Sheet 2 United States Patent O 3,295,077 CURRENT ZERO SENSING AND LATCHENG ELE- MENT FOR CIRCUIT BREAKERS Howard R. Shaffer, Glenside, Pa., and .lohn C. Lucas, Cherry Hill, NJ., assignors to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Penn- Sylvania Filed Aug. 12, 1965, Ser. No. 479,072 3 Ciaims. (Cl. 335-19) This invention relates to a novel latch structure for circuit interrupters, and more specifically relates to a novel auxiliary latch element which prevents the contact opening of a circuit interrupter until prior to or at zero current magnitude through the contacts.

Circuit interrupters of the type to which the invention relates are well known to those skilled in the art. Typical of these devices is the circuit interrupter fully described in U.S. Patent 3,182,157, issued May 4, 1965, in the name of l. C. Brumlield and assigned to the assignee of the instant invention.

As illustrated therein, the circuit interrupter includes a toggle mechanism which moves a pair of cooperable contacts between their engaged and disengaged position. In order to automatically operate the toggle and thus the contacts in response to predetermined current conditions, an overload tripping mechanism and instantaneous tripping mechanism are provided for causing the operation of the toggle and thus the contacts in response to some predetermined overload current which flows for a predetermined length of time, or to some high fault current respectively. In either of these cases, a bimetal or a magnet are automatically operated to operate a common tripper bar which, in turn, permits release of the toggle mechanism and thus the opening of the contacts.

In accordance with the present invention, a current magnitude sensing means is provided in addition to the above noted automatic operating mechanisms, wherein this additional current sensing means connects an additional and auxiliary latch mechanism into the linkage leading to the toggle assembly. This latch is then operated to its unlatched position only prior to or at a zero magnitude of current through the circuit breaker contacts. Thus, the main tripper bar is initially operated responsive to an overload or fault current condition, but the toggle assembly cannot be released until the current zero sensing mechanism is operated. Therefore, the contacts will now operate immediately preceding or at a current zero, thereby substantially limiting the arc energy created when the contacts are operated.

Accordingly, the primary object of this invention is to provide an auxiliary latching mechanism for contacts which is released responsive to current Zero through the contacts.

Another object yof this invention is to substantially decrease the energy dissipated across the contacts of a circuit interrupter.

Another object of this invention is to provide a novel circuit interrupter which includes current Zero sensing means for controlling the opening of the contact, thereby permitting the use of smaller contacts.

Yet another object of this invention is to substantially decrease the required arc chute capacity of a circuit interrupter.

A still further object of this invention is to provide a novel circuit breaker of the standard type which has the need for arc chutes eliminated therefrom by the addition of an auxiliary current zero sensing and latching means.

These and other objects of this invention will become apparent from the following description when taken in connection with the drawings, in which:

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FIGURE 1 schematically illustrates the concept of the present invention.

FIGURE 2 illustrates a typical molded case circuit breaker in cross-section which is adapted with the novel structure of the invention.

FIGURE 3 is a cross-sectional view of FIGURE 2 taken across the line 3-3 in FIGURE 2.

Referring now to FIGURE 1, We have schematically illustrated therein a circuit breaker of the type specically shown in Patent No. 3,182,157 which is incorporated into the present application by reference.

Thus, as schematically shown in the drawing, the circuit interrupter will have a line terminal 10 and a load terminal 11 for one phase. Note that the circuit interrupter may be a multiphase device, although only a single phase is illustrated in the drawing.

The line terminal 10 is then connected to a stationary contact 12. The stationary contact 12 is then engageable by a movable contact 13 which is carried on a Contact arm 14 which is pivoted at a pivotal position 15.

The current path from line terminal 10 then continues from contact arm 14 to conductor 16 which is connected to a winding 17 on a magnetic core 18 which constitutes a portion of the novel current Zero sensing and latching mechanism of the invention.

The coil 17 is then electrically connected to a heater element 19 which is, in turn, connected in series with a standard instantaneous trip magnetic structure 20. The trip magnetic structure 20 is then connected to the load terminal 11. Trip magnet structure 20 is comprised of a standard magnet body and pivotally movable armature, with the armature connected, as illustrated in dotted lines, to a bimetal strip 21 which is adjacent heater 19. Bimetal 21 constitutes the overload tripping element of the device. Note that trip magnet structure 2i) could be directly connected to the main tripper bar of the device.

The operating mechanism for the circuit breaker then includes a toggle assembly which includes a link 22 which is operatively connected to the movable contact arm 14, as indicated by dotted line 23. Note that this toggle assembly is of a standard type clearly shown in the above noted Patent No. 3, 182,157, and is not necessary to be described in detail herein for an understanding of the present invention.

The link 22 of the toggle assembly which operates contact arm 14 is then latched by a latch bar 23 which is pivotally mounted on a stationary pivot 24. The lefthand end of latch bar 23 is then movable between a latched and unlatched position with respect to latch 25 of the tripper bar 26 which is pivotally mounted on stationary pivot 27.

All of the mechanism described to this point, with the exception of magnet 18 and winding 17, are of the old and well known variety. Thus, in operation, when an overload current flows through contacts 12 and 13 for a predetermined length of time, the heater 19 will generate suicient heat to cause bimetal 21 to deflect to the right, thus engaging the bottom of tripper bar 26 and rotating tripper bar 26 counterclockwise. This removes latch 25 from the left-hand end of bar 23, thereby permitting bar 23 to rotate clockwise, thus releasing the latch engagement between the right-hand end of bar 23 and the toggle link 22. This then permits the toggle assembly to collapse, whereupon the contact arm 14 is rotated counterclockwise, and contacts 12 and 13 are rapidly opened.

Note that this operation will occur arbitrarily within the current cycle. Therefore, it has been necessary in the past to make the contacts 12 and 13 suiciently large to handle the Worst anticipated arcing that could occur, and at the same time, arc chute means have been provided in order to control such arcing.

In the event that a serious fault exists on the line being protected by the circuit interrupter of the drawing, the current through contacts 12 and 13 will rise very rapidly, whereupon the instantaneous magnet trip 20 will operate to immediately deect bimetal 21 or otherwise rotate tripper bar 26, thus causing the operation as indicated above. contacts 12 and 13 operate is an arbitrary point within the current cycle.

The principle of the present invention is to provide auxiliary means for latching the operating mechanism of contacts 12 and 13 so that after the mechanism has been released in a normal manner to operate the contacts, an auxiliary latch prevents such operation until a current zero is reached, or until just prior to a current zero for the current through contacts 12 and 13.

This novel current zero sensing and latching element includes magnet 18 and its winding 17 and a further armature 31B for the magnet 18 which is pivotally mounted on a stationary pivot 31. The armature 30 then has a latching end 32 which is movable into and out of latching engagement with bar 23. In addition, the lower end of armature 30 is connected to a biasing spring 33 which is xed at its left-hand end as illustrated, thereby biasing armature 33 away from the pole faces of magnet 18 and moving the latch 32 away from normal latching engagement with the bar 23.

The magnet 1S and its winding 17 are then so designed that when the current through winding 17 exceeds the normal rated value of the circuit breaker, a suicient force will be provided to attract the lower end of armature 30 toward magnet 18, thereby moving latch 32 into latching engagement with the bar 23. As the instantaneous current through coil 17 and thus the contacts 12 and 13 decrease toward zero, however, the force applied to armature 39 will decrease in a corresponding manner, whereupon prior to current zero or at current zero, the latch 32 will completely clear bar 23, thereby permitting rotation of the bar 23 and release of the toggle assembly link 22.

Thus, in operation, and when there is a high current fault which operates instantaneous trip means 20, or an overload current which deects bimetal 21 through heater 19, the high instantaneous current magnitudes of these currents will cause the latch 32 to move into latching engagement with bar 23 along with the release of latch 25 and bar 23. Therefore, the operating mechanism is capable of moving contact arm 14 to the open position, except for the presence of latch element 32. Latch element 32 is then retained in position, responsive to the instantaneous current through contacts 12 and 13 and will be removed when this current decreases to some predetermined value suiiicient to permit spring 33 to rotate armature 3@ and thus release latch 32.

Therefore, when the contacts 12 and 13 ultimately operate, they will operate either at current zero or just prior to a current zero value, thereby substantially decreasing the amount of arc energy generated by the separating contacts 12 and 13.

It is to be noted that there is a time lag between the release of latch 32 and the actual opening of contacts 12 and 13, due to the mechanical inertia of the system. This inertia, however, is usefully applied to timing the interval between the release of latch 32 and the actual operation of contacts 12 and 13, since the latch 32 will actually release at an instantaneous current value somewhat higher than the current value which should be interrupted by contacts 12 and 13. Thus, a calculable time delay will exist due to inertia in the toggle assembly and the various linkages extending from bar 23 to contact arm 14. Hence, it is possible to cause the latch 32 to be removed at an instantaneous current which could be some predetermined value greater than current zero with the contacts 12 and 13 being actually opened at this current zero value.

Note that the spring 33 which biases armature 30 is Here again, however, the exact point at which particularly useful in preventing armature chatter of armature 30 by preventing the motion of armature 30 at currents below the nominal rated current of the circuit breaker. In addition, further latching means could extend from tripper bar 26 to armature 30 to hold armature 30 and latch 32 in engagement with bar 23 until the tripper bar 26 rotates to its unlatched position. This would eliminate armature chatter.

Moreover, in order to reduce the impedance of the current Zero sensing and latching winding 17, the magnet structure 1S can be designed to saturate at some current value higher than the drop-out value of the circuit intcrrupter.

Where the device of the drawing is used in a multipole circuit breaker application, it will be also clear that the tripper bars 26 for each pole could be interconnected so that all of the latches equivalent to latch 25 would release at the same time whenever there is a fault on any pole. The individual latch 32 of the faulted pole, however is released only at the curent zero value, while the remaining poles operate normally within their rated current values.

FIGURES 2 and 3 illustrate one manner in which the structure schematically described in FIGURE l can be put into practice. More specifically, FIGURES 2 and 3 illustrate a circuit breaker having a molded housing which, in FIGURE 2, has been broken away to illustrate the internal mechanism of the circuit breaker.

Referring to FIGURE 2, the circuit breaker includes a pair of terminals 51 and 52 wherein the terminal 51 is connected to a stationary contact 53. Stationary contact 53 then cooperates with a movable contact arm 54 which is pivotally rotatable on the pivot 55. Movable contact arm 54 is then connected to the conductor 56 by pigtail 57. The conductor 56 then passes through the magnetic auxiliary latch `of the invention, as will be described more fully hereinafter.

The conductive path from conductor 56 includes the conductor 57, which serves as the heater for a bimetal system 90. In addition, conductor 57 can cooperate with instantaneous magnetic trip system 5S, which is suitably pivotally mounted and biased clockwise by biasing spring 59.

The right-hand end of conductor 57 is then connected to the terminal 52.

In order to operate the movable contact arm 54, a suitable toggle mechanism 60 is provided which can be manually operated by handle 61 in the usual manner. The toggle mechanism 69 further includes a trip latch 62 which is pivotally mounted on the pivot 63, and latches against the latch bar 64 of a rotatable tripper bar 65 carried on pivot 66.

The tripper bar 65 is rotatable in a clockwise direction to release latch bar 64 and latch 62, whereupon the toggle mechanism 60 can collapse to permit automatic opening of contact 54 in response to fault currents.

The tripper bar 65 is operated when the end of screw 91, carried in bimetal 90, strikes the projection 92 of the tripper bar 65. The bimetal 90 is caused to move by being suiiciently heated by an overload current, which ilows for a sulhciently long time to dellect screw 91 into projection 92, thereby causing the contacts of the interrupter to open. Alternatively, a suitable instantaneous trip could have resulted, as member 58 is strongly attracted toward conductor 57 due to the very high short circuit current low. The tripper bar 65 is operated when the end of screw 67, carried in member 58, strikes the projection 63 of the tripper bar 65.

In accordance with the invention, even though tripper bar 65 is rotated to release latch member 64, auxiliary means prevent the movement `of latch 62 until current zero or until prior to a current zero value.

Thus, in accordance with the invention, a suitable support frame is provided which includes magnetic side plates and 71 which form a magnetic path through a pivotally mounted magnetic armature 72. Thus, support plates 73 and 74 have suitable aligned openings such as opening 75, shown in FIGURE 3, which receive an extending projection of armature 72, thereby to pivotally mount armature 72, as seen in FIGURE 3.

Plate 74 then has an extending ledge 79 which receives an adjustment spring support screw 76 which receives one end of spring 77. The opposite end of spring 77 is then connected to normally bias armature 74 upwardly and into engagement with a stop 78 (FIGURE 2), which is dened at the end of support plate 73.

The armature 72 further carries a projecting arm 80, the end of which is movable immediately beneath latch 62. The armature 72 and latch 80 are shown in FIG- URES 2 and 3 in position under abnormal current conditions. In normal current carrying conditions, the spring 77 will bias armature 72 upwardly so that the upper end of latch arm 80 clears the bottom of latch 62 so that the latch 62 can be moved.

If now an abnormal current condition occurs, the conductor 57 passing between magnetic plates '76B and 71 will cause a magnetic eld suiciently strong to move armature 72 to the position shown, whereby latch 30 is positioned beneath latch 62.

The tripper bar 65 is then actuated by the thermal or instantaneous trip elements and rotated counterclockwise, thereby to release latch 62 except for the presence of additional latch S0. The additional latch S0 will now move out of blocking position only when the current through conductor 57 has decreased toward a current zero value, whereupon the latch 62 may complete its clockwise rotation with the contacts 53 and 54 disengaging when the current therethrough reaches the zero value.

Although this invention has been described with respect to its preferred embodiments, it should be understood that many variations and modifications will now be obvious to those skilled in the art, and it is preferred, therefore, that the scope iof the invention be limited not by the specific disclosure herein but only by the appended claims.

The embodiments of the invention in which an eX- clusive privilege or property is claimed are defined as follows:

1. A latch mechanism for a circuit breaker; said circuit breaker including a pair of cooperable contacts, a latchable operating mechanism connected to one of said contacts for moving said one of said contacts between an engaged and disengaged position, and an automatic current responsive trip means; said latch mechanism comprising a first latch means, an auxiliary latch means and a current magnitude sensing means; said rst latch means connected from said automatic current responsive trip means to said latchable operating mechanism and being movable between a latching and unlatching position with respect to said latchable operating mechanism; said current magnitude sensing means including circuit means connected in series with said pair of cooperable contacts; said auxiliary latching means being connected to said latchable operating mechanism and being movable between a latching position and unlatching position responsive to the current magnitude through said current magnitude sensing means; said auxiliary latching means moving to its said unlatching position after said rst latch means moves to its said unlatching position and responsive to a predetermined current magnitude which will decay to a substantially zero value at the time said latchable operating mechanism moves said cooperable contacts to their said disengaged position.

2. The device substantially as set forth in claim 1 wherein said automatic current responsive trip means includes an overcurrent trip responsive means and an instantaneous current trip responsive means.

3. The device substantially as set forth in claim 1 wherein said auxiliary latching means includes a magnet having a winding thereon connected in series with said cooperabie contacts, and a movable armature biasing means connected to said armature to normally hold said armature spaced from said magnet; said armature being moved into latching engagement with said latchable `operating mechanism when the current through said winding exceeds some predetermined value.

No references cited.

BERNARD A. GILHEANY, Primary Examiner.

R. N. ENVALL, Examiner. 

1. A LATCH MECHANISM FOR CIRCUIT BREAKER; SAID CIRCUIT BREAKER INCLUDING A PAIR OF COOPERABLE CONTACTS, A LATCHABLE OPERATING MECHANISM CONNECTED TO ONE OF SAID CONTACTS FOR MOVING SAID ONE OF SAID CONTACTS BETWEEN AN ENGAGED AND DISENGAGED POSITION, AND AN AUTOMATIC CURRENT RSPONSIVE TRIP MEANS; SAID LATCH MECHANISM COMPRISING A FIRST LATCH MEANS, AN AUXILIARY LATCH MEANS AND A CURRENT MAGNITUDE SENSING MEANS; SAID FIRST LATCH MEANS CONNECTED FROM SAID AUTOMATIC CURRENT RESPONSIVE TRIP MEANS TO SAID LATCHABLE OPERATING MECHANISM AND BEING MOVABLE BETWEEN A LATCHING AND UNLATCHING POSITION WITH RESPECT TO SAID LATCHABLE OPERATING MECHANISM; SAID CURRENT MAGNITUDE SENSING MEANS INCLUDING CIRCUIT MEANS CONNECTED IN SERIES WITH SAID PAIR OF COOPERABLE CONTACTS; SAID AUXILIARY LATCHING MEANS BEING CONNECTED TO SAID LATACHABLE OPERATING MECHANISM AND BEING MOVABLE BETWEEN A LATCHING POSITION AND UNLATCHING POSITION RESPONSIVE TO THE CURRENT MAGNITUDE THROUGH SAID CURRENT MAGNITUDE SENSING MEANS; SAID AUXILIARY LATCHING MEANS MOVING TO ITS SAID UNLATCHING POSITION AFTER SAID FIRST LATCH MEANS MOVES TO ITS UNLATCHING POSITION AND RESPONSIVE TO A PREDTEREMINED CURRENT MAGNITUDE WHICH WILL DECAY TO A SUBSTANTIALLY ZERO VALUE AT THE TIME SAID LATCHABLE OPERATING MECHANISM MOVES SAID COOPERABLE CONTACTS TO THEIR SAID DISENGAGED POSITION. 